The present invention relates to a method of manufacturing liquid crystal display units. More particularly, the invention relates to a method for manufacturing a liquid crystal display unit in which the probability of, in the manufacture of a large-area high-resolution liquid crystal display unit, the gate electrode lines being broken is reduced.
In a liquid crystal display unit, in general, a display material such as liquid crystal is held between two substrates. A voltage is applied to the display material to effect the ,desired display. To this end, picture element electrodes are arranged in matrix form on at least one of the two substrates, and active elements such as FETs (field-effect transistors) having a nonlinear characteristic are provided for the respective picture element electrodes with which the picture element electrodes are selectively activated.
A conventional liquid crystal display unit of this type is shown in FIGS. 1, 2 and 3. FIG. 1 is a plan view showing essential components of a TFT array substrate formed according to a conventional liquid crystal display unit manufacturing method. FIGS. 2 and 3 are sectional views taken along lines II--II and III--III, respectively, in FIG. 1.
In these figures, reference numeral 1 designates a transparent insulated substrate; 2, a gate electrode line used to form gate electrodes; 3, a source electrode line used to form source electrodes; 4, a drain electrode; 5, a display electrode such as a picture element electrode; 6, a gate insulating film; 7, a semiconductor layer; 8, a passivation film; 9, a light shielding film; and 10, a contact part between the drain electrode 4 and the picture element electrode 5. In this unit, a plurality of gate electrode lines 2 and a plurality of source electrode lines 3 are arranged in such a manner that the source electrode lines 3 cross the gate electrode lines 2. At each of the intersections of the lines 2 and 3, the drain electrode 4, the gate insulating film 6, the semiconductor layer 7, the gate electrode 2 and the source electrode 3 form a nonlinear type active element. The active elements and the picture element electrodes 5 form the TFT array substrate.
The TFT array substrate confronts an electrode substrate (not shown) with liquid crystal or the like held therebetween, thus forming a liquid crystal display unit. A transparent conductive film is formed on the confronting electrode substrate.
The gate electrodes 2 of the TFT array substrate employed, for instance, in a liquid crystal display unit is, in general, made of a high-melting-point metal such as Cr for the purpose of preventing picture element defects due to the occurrence of cracks. The high melting-point metal has a high resistivity, and therefore the film thickness is of the order of 2000 .ANG. at the maximum. However, in the formation of a large-screen high-resolution display unit, the film thickness should be of the order of 3000 .ANG. to prevent the signals from being attenuated by the circuit resistance and to allow high frequency operations.
In the conventional liquid crystal display described above, if the thickness of the gate electrode lines is increased to about 3000 .ANG., the probability of cracks forming is increased. Moreover, in order to increase the resolution, the wiring should be made finer. However, if in the manufacture of liquid crystal display units the patterning is unsatisfactory due to the presence of dust or the like, the wires have a greater tendency to break, thus lowering the yield.